1. Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device exhibiting improved emission performance and high electrostatic breakdown voltage due to strain relaxation in a light-emitting layer by forming a pit on an n-type layer, wherein AlGaN is used as a barrier layer of the light-emitting layer.
2. Background Art
As a Group III nitride semiconductor light-emitting device, a structure has been known in which a pit is formed on an n-type layer, and a light-emitting layer is formed without burying the pit.
For example, Japanese Patent Application Laid-Open (kokai) No. 2007-180495 discloses that an ESD layer comprising two layers: i-GaN layer and n-GaN layer, is provided on an n contact layer, a pit is formed on the i-GaN layer, and Si concentration and film thickness of the n-GaN layer are controlled to fall within a specified range, thereby high electrostatic breakdown voltage is attained. It is also disclosed that a light-emitting layer has a MQW structure in which AlGaN is used as a barrier layer.
Japanese Patent Application Laid-Open (kokai) No. 2007-201424 discloses a Group III nitride semiconductor light-emitting device wherein an intermediate layer having a pit with a top diameter of 0.05 μm or more is formed on an n-type layer, and a light-emitting layer is formed thereon without burying the pit, thereby suppressing the reverse current when current flows. It is also disclosed that the light-emitting layer has a MQW structure in which GaN and InGaN are alternately deposited.
Japanese Patent Application Laid-Open (kokai) No. 1999-220169 describes that a layer having a pit is formed between a growth substrate and a light-emitting layer, thereby relaxing the strain in the light-emitting layer and improving emission performance.
Attempts have been made to improve emission performance by using AlGaN as a barrier layer so that the electrons are more efficiently confined in a light-emitting layer having a MQW structure of Group III nitride semiconductor light-emitting device. However, when a pit is formed on an n-type layer and AlGaN is used as a barrier layer of the light-emitting layer, there is the following problem. When the pit diameter is excessively small, the strain in the light-emitting layer is not sufficiently relaxed, resulting in the reduction of light output. On the other hand, when the pit diameter is excessively large, the carriers are not sufficiently confined, resulting in the reduction of emission performance.
Japanese Patent Application Laid-Open (kokai) No. 2007-180495 discloses that AlGaN is used as a barrier layer of a light-emitting layer, but there is no consideration for the pit diameter. In Japanese Patent Application Laid-Open (kokai) No. 2007-201424, the pit diameter is examined when GaN is used as a barrier layer of a light-emitting layer, but there is no mention of the pit diameter when AlGaN is used.